Origin of life research is the study of how life came to be as a transition from non-life to life in the vastly different early Earth environment. What happened 4 billion years ago before LUCA? Abiogenesis is the scientific hypothesis for origin of life explaining a natural process by which life arises from non-living matter, such as simple organic compounds. Abiogenesis asks: how did pre-life chemical reactions give rise to life? Ideas such as RNA World hypothesis, “metabolism-first” hypotheses, the 1952 Miller–Urey experiment, Warm Little Pond, and Primordial Soup, seek to answer this question. Panspermia is the idea that life may have originated elsewhere in the universe and came to Earth: amino acids (the building blocks necessary for life) have been found in meteorites, comets, asteroids, and star-forming regions of space.
The adult human brain weighs on average about 1.2–1.4 kg (2.6–3.1 lb) which is about 2% of the total body weight. Although the human brain represents only 2% of the body weight, it receives 15% of the cardiac output from the heart, 20% of total body oxygen consumption, and 25% of total body glucose utilization. The brain consumes up to 20% of the energy used by the human body, more than any other organ. Brain metabolism normally relies upon blood glucose as an energy source, but during times of low glucose (such as fasting, endurance exercise, or limited carbohydrate intake), the brain uses ketone bodies for fuel with a smaller need for glucose.
Bonus fact: The adult human brain is estimated to contain 86±8 billion neurons.
A neutron star is so dense that one teaspoon of its material would have a mass over 5,500,000,000 tonnes (5.5 billion), about 900 times the mass of the Great Pyramid of Giza (often cited as 5.9 million tons / 5.3 million tonnes). At the extraordinarily high densities of neutron stars, ordinary matter is squeezed to nuclear densities. All of that matter is packed into a radius on the order of 10 kilometers (6 miles). Bonus fact: There are a number of sub-types of neutron stars, such as pulsars, magnetars, both pulsars and magnetars, x-ray pulsars, and more.
400 million years ago, in the Devonian period, cartilaginous fishes such as primitive sharks became more numerous. The first tree dates to about 385 million years ago, and the Dinosaur Age started 252 million years ago, making sharks older than trees and dinosaurs. One galactic year (the duration of time required for the Sun to orbit once around the center of the Milky Way Galaxy) is approximately 225 million Earth years, meaning that sharks have been around for two complete galactic years. Bonus fact: Sharks and rays rely on electrolocation to detect the electromagnetic field of living things nearby. The shark has the greatest electrical sensitivity of any animal. Sharks can find prey hidden in sand by detecting the electric fields.
Evidence is mounting that loggerhead turtles use a form of navigation termed Magnetoreception. This allows them to sense the Earth’s magnetic field. It has been observed that young loggerhead turtles inherit a magnetic map and magnetic compass sense that guides their first transoceanic migration. The turtles change their migration direction due to the magnetic fields in key ocean areas. Most sea turtle species migrate over significant distances to nesting or foraging grounds, some even crossing entire ocean basins.
